Cyg X-3: can the compact object be a black hole?

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By means of population synthesis we find that the expected Galactic number of black holes with massive helium star companions is 100 and depends on an assumed threshold for Mpre-BH. The overwhelming majority of these systems has orbital periods in excess of 10 hr, with a maximum at 100 hr, while under the Illarionov & Sunyaev (1975) disk formation criteria for accretion from the strong stellar wind of Wolf-Rayet star disk accretion is possible only for orbital periods below 10 hr. However, the number of such short-period systems is vanishingly small. If the accretor in Cyg X-3 is a 10 Mₛun black hole, then the accretion rate will be super-Eddington. Super-Eddington accretion may be responsible for the formation of jets in Cyg X-3 and may also support an X-ray luminosity as high as 10³⁹ erg/s. From the orbital period distribution for neutron stars with massive helium companions we find that if during the common envelope phase a neutron star accretes at Eddington rate and spins-up to the equilibrium period, then in most systems it acts as a ``propeller'' and accretion from the WR star wind is impossible. For the model with two massive helium stars as an immediate progenitor of Cyg X-3, requirement of accomodation of two WR stars in the post-common-envelope orbit combined with severe mass loss by them prevents formation of BH+WR systems with orbital periods less than several days.